This invention relates to an apparatus and method for an evaporative fluid cooler as a closed circuit cooling tower or as an evaporative condenser, in which an alternative coil circuiting arrangement is used to cool a the fluid or condense a gas in the closed loop.
The prior art includes the use of closed loop cooling towers for applications relating to industrial process cooling. Open circuit cooling towers have been used for large chilled water systems for many years. More recently, closed circuit cooling towers have been used for condenser water cooling systems for packaged chillers. Closed circuit cooling towers are also used on systems with many small, hard to clean heat exchangers, such as water source heat pumps and welding machines.
In a typical coil tube arrangement for a closed circuit cooling tower, circuits are provided between an upper header with a fluid inlet nozzle and a lower header with a fluid outlet nozzle. The individual circuits extend from the upper header to the lower header in a serpentine arrangement, which may be generally described as a series of parallel straight tube lengths connected by unshaped bends. Fluid has historically been communicated from the top of the coil tube assembly, or upper header, to the lower header by traversing the plurality of parallel tube lengths. However, in certain applications, the fluid flow through the coil tube assembly can be upwardly from a lower header to the upper header.
The fluid to be cooled is circulated inside the tubes of the bundle. Heat flows from the process fluid through the coil tube wall to the water cascading over the tubes from a spray-water distribution system. Air is forced upwardly or across or even downwardly over the coil depending on the specific configuration, evaporating a small percentage of the water, absorbing the latent heat of vaporization and discharging the heat to the atmosphere. The remaining water is recovered in a tower sump for recirculation to the water spray system. Liquid water droplets entrained in the air stream are recaptured in mist eliminators at the unit discharge and returned to the sump. Advances in evaporative coil product technology have led to higher thermal capacities per individual circuit unit. This higher flow capability has also resulted in an increase in tube bundle pressure drop with the traditional “double” serpentine bundles, where a grouping of two rows of circuits is fed from a common header. To solve the pressure drop dilemma, so-called “QUAD” serpentine bundles were developed, where groupings of four rows of circuits are fed from a common header, significantly lowering pressure drop, but simultaneously lowering thermal performance and increasing cost. In the designs for QUAD serpentine bundles, thermal performance is reduced due to the lower tube velocity, which results in a lower internal film heat transfer coefficient. In addition, fewer passes of the fluid to be cooled through the spray water chambers reduces the potential heat transfer. Performance is also negatively impacted as the heated spray water from one circuit falls onto a lower circuit below that is fed with the same temperature fluid. Cost is increased due to the greater number of circuits in a QUAD bundle (usually about twice that of double serpentine bundles), which must then be fabricated and welded into both the upper and lower headers, offset by the reduced length of individual circuits which make the individual circuits easier to bend. Additionally, multiple connections would often be required to accommodate the coil flow on the standard serpentine, leading to increased coil cost and installed cost for higher flow applications.
The prior art described above suffers various deficiencies in its application to closed circuit cooling towers. There is a need for a relatively simple and inexpensive coil circuiting arrangement for a closed circuit cooling tower that can maintain a relatively low pressure drop, but without simultaneously lowering thermal performance by a significant degree.